The present disclosure relates to determining the magnitude of a power take off unit and adapting a drive train of a heavy commercial vehicle based on the presence of an additional load of the power take off unit.
Heavy commercial vehicles such as overland trucks and buses are known to employ automatic mechanical transmissions (AMT) that are based on preprogrammed routines. One example of an automatic mechanical transmission is the multi-stage gearbox. A multi-stage gearbox is usually made up of an input shaft, an intermediate shaft, which has at least one gearwheel in engagement with a gearwheel on the input shaft, and a main shaft with gearwheels which engage with gearwheels on the intermediate shaft. The main shaft is also connected to an output shaft coupled to the driving wheels via, for example, a drive shaft. Each pair of gearwheels has a different ratio compared with another pair of gearwheels in the gearbox. Different gears are obtained by virtue of different pairs of gearwheels transmitting the torque from the engine to the driving wheels.
One of the problems in controlling an AMT, however, is attributable to the power consumption by a power take off (PTO). A PTO can generally be classified as a PTO upstream or downstream of the master clutch, hi general, a PTO that is upstream of the master clutch can take power from the vehicle's engine regardless of the state of engagement of the transmission via the master clutch. A PTO that is located downstream of the master clutch is typically used when the vehicle is stationary. A downstream PTO often involves placing the gearbox in neutral so that the vehicle wheels are not drivingly engaged to the transmission. However, there are cases when a transmission mounted PTO is used while the vehicle is in motion. PTOs are known to impose significant load on the vehicle's engine. Exemplary PTOs use engine power to drive PTO connected hydraulic pumps that can be activated for such things as mixing applications (concrete trucks) or causing motion of a bed on the truck such as in the case of dump trucks and flat-bed haulers.
Similarly, PTOs may be used to power spreaders such as those used to broadcast salt or sand on icy roads, or to power associated trailer components such as compartment refrigeration units. While these examples are not exhaustive, they do serve to exemplify PTO loads of significant magnitude which can appreciably compromise the driving power available from the engine of the vehicle for the drive wheels, and which often causes undesirable disturbances to automated transmission programs that do not take their intermittent influences into account. For purposes of comparison, these significant PTO loads can be compared to less influential engine loads imposed by such power consumers as cooling fans and air conditioning compressors. As an example of the potential drag that a PTO can impose on the vehicle's engine, it is not uncommon for PTOs to siphon off engine torque on the order of 5 to 3000 Nm. An example of a PTO that requires on the order of 3000 Nm is a fire truck that operates a water pump, and an example of a PTO that requires on the order of 5 Nm is a PTO for a small refrigerator device.
The present invention appreciates the fact that transmission control routines that do not take into consideration whether or not a significant PTO load is imposed on the vehicle's engine will experience degradation in performance when the PTOs are operational. For example, if the PTO loads are of such magnitude that the engine can not compensate therefore by increased engine speed, there will be an effective reduction in power available for driving the vehicle. The strategy must, however, appreciate that the behavior of the PTO-loaded engine is not that of a smaller engine, but is in fact a unique behavior of the particular engine whose power is divided between a PTO of significant load and the drivetrain.
In at least one embodiment, the present invention takes the form of a method for adjusting drivetrain control of a vehicle. Said vehicle drivetrain comprises a prime mover connected to a transmission and a power take off unit driven by said prime mover. The method is characterized in continually during vehicle driving determining a torque magnitude indicative of said power take off unit's torque consumption by sensing a fluid pressure produced by a power take off fluid pump for driving a power take off unit power consumer with variable or constant power need. The method is further characterized in continually comparing the sensed power take off unit torque consumption with an output torque produced by said prime mover and adjusting operation of the drivetrain in consideration of, a by said power take off unit, reduced torque available for application to an output shaft of the transmission under driving conditions.
An advantage of the invention is that a better operation can be performed by the automatic transmission and/or the prime mover. This results in better comfort and efficiency. In another embodiment of the invention the determined torque magnitude of the power take off unit is used for adapting gear selection of the automatic transmission.
In a further embodiment of the invention said power take off fluid pump is a constant displacement pump.
In another embodiment of the invention said prime mover is one of a diesel engine, a gasoline engine, an electric engine, and a hybrid engine.
In another embodiment of the invention said transmission is an automatic transmission.
Further advantageous embodiments of the invention are disclosed herein.